1. Field of the Invention
The present invention relates to a light guide plate, a surface light source device, and a transmission image display device.
2. Related Background Art
A transmission image display device such as a liquid crystal display device generally has a surface light source device for supplying surface light using a light guide plate, as a backlight. Types of surface light source devices include a direct backlight type in which the light source is located on the back side of the light guide plate, and an edge light type in which the light source is located along a side face of the light guide plate. The edge light system is advantageous in terms of reduction in thickness of the image display device.
In the surface light source device of the edge light type, the light incident through the side face of the light guide plate is diffused by action of a light distribution pattern provided on the back side of the light guide plate (e.g., a light distribution pattern comprised of light scattering dots), and light components with angles of not less than the critical angle emerge from an exit surface of the light guide plate, thereby supplying the surface light. For making the luminance of its light emission surface uniform, the light guide plates described in Patent Literatures 1 and 2 below are provided with such gradation as to change the density of the light distribution pattern from coarse to dense with distance from the light source.
Patent Literature 1 also discloses a technique of forming the light distribution pattern of the dot pattern by ejection of liquid droplets (e.g., by ink jet printing).
Patent Literature 1: Japanese Patent Application Laid-open No. 2004-240294
Patent Literature 2: Japanese Patent Application Laid-open No. 2008-27609